This invention relates to an energy absorber for a motor vehicle steering column.
A typical energy absorbing steering column on a motor vehicle includes a housing or mast jacket which translates linearly through a collapse stroke during a collision of the motor vehicle with another object when a steering hand wheel on the steering column is impacted by the operator of the motor vehicle. The mast jacket translates against a resisting force produced by an energy absorber which converts into work a fraction of the kinetic energy of the operator. Commonly, the resisting force is created by plastic deformation of a metal element of the energy absorber. For example, in the energy absorber described in U.S. Pat. No. 3,392,599, steel spheres plastically deform a metal mast jacket by rolling tracks in the mast jacket. In other prior energy absorbers, a flat metal strap is plastically deformed by being pulled over a stationary anvil or vice versa. Optimal performance of such energy absorbers is achieved when the kinetic energy of the operator is completely converted into work at the completion of the maximum collapse stroke of the mast jacket. However, because these energy absorbers are not adjustable after the steering column is assembled but operators of differing weight often operate the motor vehicle, optimal energy absorbing performance may not always occur. U.S. Pat. No. 4,886,295 describes an energy absorbing motor vehicle steering column having an energy absorber which is actively variable during operation of the motor vehicle for more optimal energy absorbing performance and which includes a plurality of roll deformers in an annulus between an inner tube and a longitudinally split outer tube. An expandable bag having fluid therein is disposed around the split outer. A control system which monitors control variables characteristic of the kinetic energy of an operator of the motor vehicle controls the fluid pressure in the bag and, therefore, the interference fit of the roll deformers between the inner and outer tubes, to optimize the performance of the energy absorber.
This invention is a new and improved actively variable energy absorber including a convex anvil on one of a steering column housing and a steering column support, a flat metal strap attached to the other of the steering column housing and the steering column support and slidably engaging the convex anvil on an active surface area of the convex anvil, and a control apparatus for actively varying the geometric relationship between the flat metal strap and the convex anvil in response to changes in a control variable thereby to adjust the magnitude of the active surface area. Adjusting the magnitude of the active surface area changes the severity of plastic deformation of the flat metal strap and the magnitude of the friction between the flat metal strap and the convex anvil thereby to adjust the force resisting linear translation of the steering column housing and the corresponding performance of the energy absorber. In some embodiments of the actively variable energy absorber according to this invention, the flat metal strap is plastically deformed by being pulled over a single convex anvil during linear translation of the steering column housing. In other embodiments of the energy absorber according to this invention, the flat metal strap is plastically deformed by being pulled across a plurality of convex anvils or by being pulled edgewise between a pair convex anvils.